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    Performance.now()

    Summary

    The Performance.now() method returns a DOMHighResTimeStamp, measured in milliseconds, accurate to one thousandth of a millisecond.

    The value represented by 0 varies according the context:

    • in shared or service workers, the epoch represents the moment the worker started.
    • outside workers, or in dedicated workers created from a Window context, the epoch is the value of the PerformanceTiming.navigationStart property.
    • in dedicated workers created from another worker, the epoch is set to the one of this other worker.

    Syntax

    t = performance.now();

    Example

    var t0 = performance.now();
    doSomething();
    var t1 = performance.now();
    console.log("Call to doSomething took " + (t1 - t0) + " milliseconds.")
    

    Unlike other timing data available to JavaScript (for example Date.now), the timestamps returned by Performance.now() are not limited to one-millisecond resolution. Instead, they represent times as floating-point numbers with up to microsecond precision.

    Also unlike Date.now, the values returned by Performance.now() always increase at a constant rate, independent of the system clock (which might be adjusted manually or skewed by software like NTP).

    Specifications

    Specification Status Comment
    High Resolution Time
    The definition of 'Performance.now()' in that specification.
    Recommendation Initial definition

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support 20.0 webkit
    24.0 [1]
    15.0 (15.0) 10.0 15.0 8.0
    on Web workers 33 34.0 (34.0) ? ? ?
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support 4.0 25.0 15.0 (15.0) 10.0 Not supported Not supported
    on Web workers ? ? 34.0 (34.0) ? ? ?

     

    [1] Windows version of Chrome 20 through 33, at the time of this writing, returns performance.now() only to millisecond precision.

    See also

    Document Tags and Contributors

    Last updated by: jpmedley,